Crosslinked silicone rubber particles possess a number of desirable chemical and physical properties including, for example, good thermal stability, elasticity, water resistance, and lubrication assistance. Because of these properties, silicone rubber particles have been proposed for a variety of applications, such as for example, impact strength improvers, low temperature flexibilizers, and processing aids for molding materials, laminates and rubber-modified plastics. Despite these beneficial properties, silicone-containing polymers possess significantly different chemical and thermodynamic properties from the other materials to which they would advantageously be intended to be added. These differences may result in compatability and dispersion problems on such application.
Methods for making crosslinked silicone rubber particles are known. Traditionally, these particles have been made commercially by grinding or cryogenically fracturing crosslinked silicone rubber, such as crosslinked silicone rubber sheets, into powder form. See Japanese Kokai JP 60-81, 227 Powdered Granular Silicone; Soviet Union Patent No. 952895 and Silicone Rubber in Powder Form, Swanson, Leicht and Wegener, American Chemical Society, Rubber Division, October 1974.
These conventional techniques possess a number of drawbacks. In addition to the expense of such techniques, which makes the particles so produced too costly for many potentially attractive commercial applications, these techniques produce a less than optimum yield of irregularly shaped particles having a wide and relatively uncontrolled range of particle sizes. It has thus become an object of workers in this art to develop more efficient and less expensive means for making crosslinked silicone rubber particles of uniform spherical shape, small particle size and narrow particle size distribution.